CBN is the second hardest known material after diamond. It is synthesised from boron and nitrogen in a
high-pressure and high-temperature process similar to the production of the synthetic diamond from which it differs by its higher thermal stability. Compared to conventional abrasives, CBN offers advantages when
grinding difficult-to-cut steels (hardness >55 HRC). Due to the low wear of the grinding wheel, high geometrical and dimensional accuracy can better be observed. Moreover, tools ground with CBN have a longer tool
life, because the cool grinding CBN hardly affects the structure of the surface zone.